1. FIELD OF THE INVENTION
The invention relates to a method for the prevention of balling during drilling, completion and workover of subterranean oil and gas wells and to the lubrication of well drilling equipment, as well as to an additive for such use.
2. DESCRIPTION OF THE PRIOR ART
When drilling, completing or working over subterranean wells in order to tap deposits of, for example, oil or gas, and in particular when utilizing a rotary drilling method comprising a bit to which is attached a drill stem, the bit will penetrate the formation. The formation is composed of both inorganic and organic substances, such as clays and other minerals as well as fossils, peat etc. As the drill bit teeth penetrate the formation, drill chips are generated by the action of the bit. These drill chips are wetted by the drilling fluid which can produce sticky, plastic fragments. These fragments adhere to the bit surface and the force and weight of the bit extrudes the water from the plastic fragments forming a compacted mass of the formation onto the bit surface that interferes with the cutting action of the bit teeth as evidenced by a reduction in penetration rate. Balling also occurs on drill collars and stabilizers
Bit balling resulting in the compaction and adherence of drill chips to the face of the cutters and the bit is a primary cause of reduction of penetration rate during drilling operations. Bit balling is believed to be the result of the adhesive forces between shale and the bit surface which become significant when ductile shales deform and are forced into intimate contact with each other and the bit surface.
A liquid adheres to a solid surface if the attraction of the molecules to the solid surface is greater than their attraction to each other, i.e., the work of adhesion is greater than the work of cohesion. This criterion may be expressed thermodynamically as: EQU W.sub.A =F.sub.S +F.sub.L -F.sub.I
Where W.sub.A is the work of adhesion; F.sub.S is the surface free energy of the solid; F.sub.L is the surface free energy of the liquid; and F.sub.I is the surface free energy of the newly formed interface. In terms of this expression, the work of cohesion, (WC), is In terms of this expression, the work of cohesion, (W.sub.C), is equal to 2 x F.sub.L.
In order for adhesion to occur between the solid surface and a liquid, the work of adhesion must be greater than that of cohesion: EQU W.sub.A -W.sub.C =F.sub.S -F.sub.L -F.sub.I
Accordingly, adhesion of the liquid to a solid occurs when the surface free energy of the solid surface exceeds that of the liquid and interface: EQU F.sub.S &gt;F.sub.L +F.sub.I
Shales adhere to bits and drill collars if they are forced into intimate contact by the force and weight of the drill string. The mechanism of adhesion in this instance is probably hydrogen bonding extending from the molecular layers of water absorbed on the surface of the shale surface to the layer of water adhering to the water-wet steel surface of the bit.
In the past, those skilled in the art have particularly relied upon use of oil-based or water-in-oil (invert emulsions) drilling fluids to eliminate or control bit balling although several aqueous based fluids and additives have been contemplated by those skilled in the art. The environmental problems and costs associated with the use of oil-based or invert emulsion systems have discouraged and/or prohibited their use on many wells.
Accordingly, the present invention addresses the problem set forth above by providing an aqueous based fluid containing therein a material which acts as a synthetic oily-like substance to inhibit bit balling upon metallic surfaces of drilling, completion and workover equipment.
Applicants are aware of the following prior art relating to the general subject area of this invention:
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